High Performance Inkjet‐Printed Quantum‐Dot Light‐Emitting Diodes with High Operational Stability

Abstract

Improving the stability of inkjet‐printed quantum dot light emitting diodes (QLEDs) is critical for the technology to become commercially viable. The major obstacle is the compromise between the printability of the ink system and the functionality of the carrier transport layers. Here, a ternary ink system consisting of octane, 1‐cyclohexyl‐ethanol, and n‐butyl acetate is reported, which solves the erosion between the printed quantum dot ink and the underneath hole transport layer. A gradient vacuum post‐treatment is developed to accompany the ternary ink system with gradient vacuum pressures, which is helpful in forming a uniform printing layer. Based on both technologies, the inkjet‐printed R/G/B QLEDS are fabricated with high resolution patterns, showing high efficiencies and stabilities. The external quantum efficiency of R/G/B devices is 19.3%, 18.0%, and 4.4%, respectively. Correspondingly, the half operating lifetime is up to 25 178 h @ 1000 cd m−2, 20 655 h @ 1000 cd m−2, and 46 h @ 100 cd m−2, respectively. The improvements in the ink engineering and post‐treatment in this study have taken the efficiency and stability of the devices to a higher level and confirm the application prospects of printed QLEDs in the display industry.

Improvement of the efficiency and stability of inkjet‐printed green quantum dot light‐emitting diodes by controlling the extra shell of quantum dot

“…Making use of A-QD, we have realized long lifetime QLEDs by IJP with a ternary ink system. 45 The QLED performance can be further improved by QD shell engineering as reported in this paper. We expect that better performed devices can be realized with the B-QDs and the ternary ink system.…”

“…45 All printed QD layers presented a densely packed and smooth surface with a roughness less than 1 nm. 45 Since the wavelengths and PLQY of the films are similar, the difference in the device characteristics is primarily due to the variation of QD structure. The varied thickness of the shell shifts the energy levels of QD (Figure 3C), hence bringing significant changes in the charge injection.…”

“…Figure 3C schematically shows the band energy levels of all layers. All devices were fabricated under the same condition and used the same ternary QD ink system reported by our group previously 45 . All printed QD layers presented a densely packed and smooth surface with a roughness less than 1 nm 45 .…”

Patterning of quantum dot light‐emitting diodes based on IGZO films

“…Since the general solution process is prone to suffer from the coffeering effect and interlayer corrosion, the uniform and flat film quality could benefit the uniform current spreading. 7 In order to further investigate the localized current density effect and luminance stability of the device, continuous luminance distribution monitoring is performed. The luminescence microscopic images before and after 8 h constant voltage stress at 6 V is shown in Figure 3A edge effects) of the device keep changing, we used constant voltage mode for the aging to observe more details.…”

“…Quantum dot light-emitting diodes (QLEDs) have attracted much attention in the display community because of their unique optoelectronic properties, including narrow emission, low turn-on voltage, and low-cost solution process. [1][2][3] Despite tremendous efforts in improving the device performance, which is indeed at a very high level, [4][5][6][7][8][9] there are still several obstacles hindering the QLED application. 10 Among them, luminance stability and pixel patterning are essential but not being addressed much in the literature.…”